Picking up Ignition pulses on analog pins safely

I'm attempting to pick up ignition pulses off of a 6 volt ignition module to read RPM (single cylinder, four stroke engine), the battery voltage never exceeds 7.5 volts, so I was thinking of setting up a 555 timer in a monostable mode to clean up the pulses. Does anybody here have any experience with interfacing with older electronic systems? The bike is a 1972 vintage, and unfortunately I don't have access to an oscilloscope to check the signal quality.

Yes, but I was using a 12 volt ignition coil instead of 6 volt coil. You are probably going to be surprised. The voltage spikes on my 12 volt coil reached about 400 volts when the coil fired. Be prepared!

As mentioned, voltage spikes.

Maybe some variety of inductive sensor is all you need. Avoids having to tap into the ignition wiring directly.
Read up on how modern car tachs work, might give you an idea on what approach to take.

on the low side of the coil?!?! wowza. I was thinking inductive wrap but I’ve got no idea how many turns of what size wire to get an acceptable pulse that won’t burn out an input on my 'duino.

On the low side. You might need to play with an inductive wrap to see how much voltage you get. It might not take much if the impedance is high enough on the input.

the frequency on my fluke is reading a bit jumpy but .03 VAC at idle to about .1VAC near redline. I'm going to go ahead and assume that this input should be just dandy for the arduino?